This invention relates to an apparatus and method for accurately controlling the velocity of a moving member, like a print head carrier, for example, which moves along the platen of a printer, and for providing timing signals for printing uniformly spaced dots when using a wire matrix printer as the printing element, even with some variation in the velocity of the print head carrier.
Most systems of the prior art utilize a tachometer which is coupled to the drive shaft of the motor driving the print head carrier, and the tachometer is used to feed back an analog signal which is proportional to the speed of the motor. The analog signal is then compared with a reference signal in a comparator means which controls the operating speed of the motor by a variety of techniques disclosed in the prior art. One system disclosing an electronic tachometer is shown in U.S. Pat. No. 3,986,091.
The preferred embodiment of the present invention utilizes a completely digital-to-digital circuit for controlling the speed of a moving member such as a print head carrier, thereby making the control of the speed more accurate than prior art systems which employ analog circuitry.